In recent years, semiconductor devices using III-V group compound with a bandgap larger than that of Si have attracted attention. Among them, a semiconductor device using nitride semiconductor such as gallium nitride (GaN) has characteristics of being able to operate at high speed and with low loss. In addition, a power MISFET (Metal Insulator Field Effect Transistor) using GaN-based nitride semiconductor can achieve the normally-off operation and the development thereof has been advancing.
For example, the Non-Patent Document 1 listed below discloses a GaN FET having a gate insulating film made of Al2O3.